This invention relates generally to the field of electrical connectors, and particularly to a Zero Insertion Force (ZIF) socket for establishing a mechanical and electrical connection between an electronic component and a circuit substrate. More particularly, this invention relates to a BGA/LGA ZIF socket for connecting a processor package to a printed circuit board.
Electronic components, such as integrated circuits, require a large number of electrical interconnections which occupy a small space in order to communicate properly with a circuit substrate. In order to provide electrical communication between the chip and external circuitry, circuit chips are usually contained within a housing or package which supports interconnection leads, pads, and the like on one or more of its external surfaces. The contact terminals may extend from a surface of the package in the form of, for example, a pin grid array (BGA), and a land grid array (LGA). A PGA includes a plurality of pins extending from the package. A BGA includes a plurality of balls attached to a surface of the package. A BGA includes a plurality of balls attached to a surface of the package. A land grid array includes a plurality of contact pads, or lands, formed on a surface of the package. To physically secure a chip to a circuit substrate, and to provide an electrical connection between the contact terminals of the chip and corresponding traces or leads of the circuit substrate, a conductive material, such as a ball of solder, can be disposed on each contact terminal of the electronic component.
Typically, BGA devices are retained in a socket mounted on a circuit substrate, such as a printed circuit board (PCB). The socket facilitates interconnection by eliminating the need to permanently electrically connect the electronic component to the PCB. While in contact with the socket, the electronic component""s contact terminals are electrically connected to the traces or leads of the PCB. Traditionally, there is an insertion force and a retention force associated with establishing or breaking the electrical connection between the electronic component and the socket.
In multiple pin electronic components, especially those having a large number of pin terminals, such as microprocessor chips, the insertion force necessary to seat the electronic component in an associated socket can be considerable and can lead to difficulty in installation of the electronic component into the socket. However, the very features of the hall grid array device which make it attractive as a device structure (e.g., closely grouped very small contacts arranged on a hidden face) make it extremely difficult to reliably mount on a PCB without damaging the BGA, the electronic component, or both. The force required to remove the component from the socket, e.g., the force required to overcome the retention force of the connection, may also be of magnitude sufficient to cause damage or even destruction of the components.
Some conventional sockets utilize zero insertion force designs which allow for easier insertion and removal of the electronic component from the socket. Zero Insertion Force (ZIF) sockets seek to maintain sufficient electrical contact for operation and testing of the electronic component while still providing a way to easily remove the electronic component from the ZIF socket and to install the electronic component onto the ZIF socket with little or no insertion force.
Traditional direct or solderless, ZIF socket systems are known wherein a ZIF socket is soldered to a PCB and the BGA package is removably attached to the ZIF socket and retained without soldering of the contact balls. Traditionally, this type of ZIF socket enables quick and easy removal, and replacement of the BGA package for repair or upgrade without soldering of the BGA adapter board. While in contact with a typical ZIF socket, an electronic component""s contact terminals are electrically connected to a circuit substrate.
Traditionally, electrical contact has been established by contact fingers, extensions, or pins that are moved between a contact and a non-contact position. The contact structures that receive the BGA contact balls typically attempt to provide sufficient electrical contact and retain the ability to articulate between the contact and non-contact position many times without jeopardizing its mechanical and electrical connection properties.
Other traditional ZIF sockets use a contact structure that is biased toward a non-contact position, and a mechanism is used to selectively move the contact structure to a contact position. When the contact terminals are inserted into the contact structure and the mechanism is used to move the contact structure, the contact structure encloses, or contacts the terminals with a low insertion force. When the conventional ZIF socket is configured to be in the closed or contact position. the electronic component is electrically connected to the circuit substrate. When the conventional ZIF socket is in the non-contact position, electrical contact between the circuit substrate and the electronic component is broken.
While beneficial in larger applications, traditional ZIF designs may not be preferred in high contact density applications. Difficulties with known ZIF sockets include complexity and cost in high contact density situations, especially when miniaturization is required. Further, the contact structures of ZIF sockets may not fit within a given footprint on the PCB. When ZIF designs are used in high contact density applications, traditional ZIF sockets have not successfully maintained the contact between the electronic component and the PCB due to solder wicketing and difficulties with conventional soldering techniques. Solder wicketing occurs when solder flows into the interior of the ZIF socket by means of a path created by a contact structure. The decreased amount of solder on the exterior of the ZIF socket often leads to a deteriorated electrical connection between the ZIF socket and the PCB. Traditional ZIF sockets do not control the solder ball during reflow, and as a result, a poor connection is formed between the ZIF socket and the PCB. Therefore, a need exists for an improved ZIF socket that overcomes the drawbacks and problems associated with electrically connecting an electronic component and a circuit substrate.
The present invention is directed to a Zero Insertion Force (ZIF) socket and method for mechanically and electrically connecting an electronic component to a circuit substrate using a substantially ZIF socket. The ZIF socket includes a housing that defines a cavity for containing a middle plate that is selectively movable relative to the housing between a contact and a non-contact position The housing includes a plurality of apertures formed in a top surface and arranged to correspond with the contact terminals of an electronic component that can be mounted on the top surface of the ZIF socket. The middle plate has a plurality of apertures formed therein and arranged to substantially correspond with the contact terminals of the electronic component. The housing also includes a plurality of apertures formed in a bottom surface and arranged to correspond with the leads or pads of a circuit substrate. The circuit substrate may also include a plurality of holes formed in the circuit substrate for receiving mounting projections extending from the bottom surface of the ZIF socket housing. An electrically connective medium such as, for example, a solder medium, is disposed between and mechanically and electrically connects the ZIF socket housing to the circuit substrate.
The ZIF socket includes a contact assembly that requires little or no insertion force to connect the contact terminal extending from the electronic component to the ZIF socket. The contact assembly has a lower portion and an upper portion. The lower portion is disposed within the apertures of the housing bottom and has an axial slot. The upper portion extends from the lower portion along an axis deviated from the axis of the lower portion and is flexible relative to the lower portion. The contact assembly can be held in place by inserting or press fitting the lower portion of the contact assembly into the housing bottom aperture so that the lower portion is subjected to a compressive force. When the contact assembly is disposed within the housing bottom aperture, the angle of the axial slot is urged to decrease by the aperture surface of the housing bottom. The housing bottom aperture holds the contact assembly lower portion so that the contact assembly is anchored in position by the compressive forces.
The contact assembly lower portion has a first portion with a longitudinal cross sectional shape corresponding to the shape of the housing bottom aperture and a second portion which is substantially conical in shape. The contact assembly lower portion has a recess in the second portion. The recess is adapted for receiving an electrically connective medium, such as a solder medium.
The present invention is also directed to a system and method of mechanically and electrically connecting an electronic component to a circuit substrate using a substantially zero insertion force socket. The system and method include mounting a ZIF socket on a circuit substrate wherein the ZIF socket is electrically and mechanically connected to the circuit substrate. The method further comprises mounting an electronic component to the ZIF socket wherein the electronic component is electrically connected to the ZIF socket by a contact assembly that requires little or no insertion force to connect the contact terminals extending from the electronic component to contact assemblies of the ZIF socket. Then the ZIF socket middle plate is moved to a contact position thereby deflecting the contact assembly into contact with the terminals of the electronic component. Each contact assembly is secured to the ZIF socket by press fitting the lower portion of the contact assembly into apertures of the ZIF socket housing so that the lower portion is subjected to a compressive force and is anchored in position by the apertures of the ZIF socket housing.
Preferably, the system and method further comprise operating the camming element to selectively move the contact assembly from a non-contact position, in which the plurality of apertures of the top and middle plates freely accept the contact terminals, and a closed position, in which the contact assemblies are in physical and electrical contact with the contact terminals thereby completing an electrical connection between the circuit substrate and the electronic component.